In traditional digital cameras, an image processing device and an image processing method is known having an imaging system wherein the photographed image goes through the lens, forms an image on the CCD where the subject image is photo electrically converted and an image signal is generated.
Next, with a single-chip CCD, an image processing device and an image processing method are known that in addition to a matrix having a plurality of photo electric conversion elements are further equipped with a color filter before it and the image data is generated after signal processing of each color pixel signal output through the color filter.
Also, in the image processing device, the color filter of the single-chip CCD is equipped with an R (red), G (green) and B (blue) 3-color Bayer array matrix for each of the photo electric conversion elements. A luminance signal and color difference signal for each unit is generated from the output signal (1 unit=1 R pixel, 2 G pixels, 1 B pixel for a total of 4 pixels) of this CCD, and a color image signal having all the color image pixels is generated from these signals (for an example see Patent Reference 1).
For example, in an image processing device equipped with the aforementioned single-chip imaging device, the R, Gr, Gb, B color signals are loaded after going through the Bayer array color filter equipped CCD (Charge Coupled Device) and then 4 pixels each of R, Gr, Gb and B are sampled and an image signal having the center pixel of the four pixels signal is generated.
In more detail, although each pixel of a single-chip CCD contains only the color information of a single color all the red (R), blue (B) and green (G) values for each pixel is necessary to display a color image. Due to this, in imaging processing that uses a single-chip CCD, a so-called demosaic process is performed based on the color mosaic image having only an R, G, or B components. The demosaic process is a process that generates a color image with each pixel having all the RGB constituents with the use of interpolation calculation on the lacking color luminance information gathered from the surrounding pixels of the corresponding color mosaic image pixels (which is called interpolation processing).
However, in image processing that uses a single-chip CCD, if only interpolation is performed then there is a danger of pseudo-color generation or loss of image resolution.
For example, as the sampling frequency of the R signal and B signal is only ½ that of the G signal, any sampling greater than fs/2 (Nyquist frequency) will be cut-off due to the sampling theorem. Also, the R signal and B single phases will, at fs/2, be out of alignment with each other.
Therefore, due to the aforementioned cut-off phase difference there is a problem of the pseudo-color (for example, formation of a stripe pattern not in the original photographed object) occurrence on both surfaces. Therefore, in order to prevent pseudo-color, there is a method in which an optical filter having a cut-off frequency of approximately fs/2 is placed between the lens and the CCD so that any light radiation greater than fs/2 is cut-off (for example, see Patent Reference 2).
Also, for the aforementioned color image processing device, there is a method of pseudo-color suppression in which, focusing on suppression of pseudo-color occurring at the image edge, the difference of the plurality of nearby pixel signals is compared and if this difference exceeds a pre-set specified value (threshold value) the pixel signal is suppressed, thus achieving pseudo-color suppression (for example, see Patent Reference 3).    Patent Reference 1: Tokukai 2000-287211 Bulletin    Patent Reference 2: Tokukai Hei 7-7733 Bulletin    Patent Reference 3: Tokukai Hei 11-308625 Bulletin